Income Taxes - Reconciliation of Tax Rate (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Statutory tax rate	12.50%	12.50%	12.50%	12.50%
International tax rates differential	(1.50%)	20.40%	6.80%	18.70%
Change in valuation allowance	(39.40%)	0.60%	(11.90%)	1.30%
Change in fair value of nondeductible contingent consideration	67.60%	(13.10%)	10.90%	(10.20%)
Nondeductible stock-based compensation	(4.70%)	0.00%	(1.80%)	0.00%
Unrecognized tax benefits	(7.60%)	0.00%	(2.80%)	0.00%
State and local income taxes, net of federal	1.00%	0.00%	0.30%	0.00%
Change in U.S. tax law	0.00%	0.00%	0.00%	0.00%
Other	(18.90%)	(0.10%)	0.60%	0.20%
Effective income tax rate	9.00%	20.30%	14.60%	22.50%
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income tax (benefit) provision - at statutory tax rate	$ (473)	$ 4,537	$ (2,293)	$ 8,843
International tax rates differential	57	7,399	(1,241)	13,259
Change in valuation allowance	1,491	230	2,181	914
Change in fair value of nondeductible contingent consideration	(2,556)	(4,757)	(2,005)	(7,232)
Nondeductible stock-based compensation	176	0	336	0
Unrecognized tax benefits	288	0	508	0
State and local income taxes, net of federal	(38)	0	(57)	0
Change in U.S. tax law	0	0	0	0
Other	713	(39)	(98)	125
Income tax (benefit) provision - at effective income tax rate	$ (342)	$ 7,370	$ (2,669)	$ 15,909